(Light Emission Source)
In a conventional light emission source in which a light emitting diode is sealed in a mold resin, light emitted from the light emitting diode to its front is emitted from the light emission source as it is, but light emitted in a diagonal direction from the light emitting diode is totally reflected on a boundary surface of the mold resin and scattered in an inside wall of a housing to be lost, resulting into deterioration of use efficiency of light.
Heretofore, there has been proposed a light emission source capable of efficiently emitting the light emitted in a diagonal direction which is disclosed in the Japanese Laid-Open Patent Publication No. Hei 1-143368. FIG. 1 shows a sectional side view of a light emission source including a light emitting diode 1, a transparent glass substrate 2, lead frames 3 and 4, a bonding wire 5, a light reflecting member 6, and a mold resin 8 made of an optically transparent resin. The lead frames 3 and 4 are disposed on a rear wall of the transparent glass substrate 2, and the light emitting diode 1 is mounted on a rear wall of the lead frame 3 to be connected with the lead frame 4 by the bonding wire 5. A light reflecting wall 7 of the light reflecting member 6 is formed as a polyhedron by plural monotonous surfaces.
In this conventional light emission source, light is emitted backside from the light emitting diode 1 to be reflected by the reflecting wall 7 and emitted forward through the mold resin 8 and the transparent glass substrate 2. In particular, light emitted from the light emitting diode 1 in a diagonal direction is reflected back by the reflection wall 7 to be emitted forward through the mold resin 8 and the transparent glass substrate 2, thereby improving the light use efficiency.
This conventional light emission source, however, has the disadvantage that light reflected by the light reflecting member is obstructed by the light emitting diode and the lead frames when it is emitted forward, thereby producing shadows of these components and deteriorating the advantage of utilization of light near the optical axis center where quantity of light should be provided most well. Furthermore, because of darkness near the optical axis center in the directivity pattern of light emitted by the light emission source, its appearance is bad as a light source for a display, and its visual performance also is bad.
FIG. 2 shows a side sectional view of conventional another light emission source, wherein a light emitting diode 1 such as an LED chip is die-bonded on a leading edge of one lead frame 3 to be connected with another lead frame 4 by means of a bonding wire 5, which is sealed in a transparent mold resin 8. On a central part of a front wall (resin boundary surface) of the mold resin 8, there is disposed a lens portion 9 so as to agree with an optical axis of the light emitting diode 1.
In this conventional light emission source of FIG. 2, the light emitting diode 1 is not positioned behind the lead frame 3, and light emitted from the light emitting diode 1 is emitted forward from the lens portion 9 without any obstruction in this conventional light emission source, however, only light emitted from the light emitting diode 1 to its front is used for external emission, thereby decreasing the use efficiency of light. Moreover, just one light emission source becomes so-called point light source, so that the light emission area cannot be enlarged.
(Photo Detector)
For example, a photodiode serving as a sensor is improved about its sensitivity as the quantity of incident light is increased, and a photoelectric transducer increases an electric energy as the quantity of incident light is increased. Accordingly, it is desirable in these photo detectors to increase the quantity of incident light as far as possible.
In order to increase the quantity of incident light when the intensity of incident light is the same, it is an approach to increase the light receiving area of the photo detector. However, this approach to increase the chip area of the photo detector reduces the number of chips which can be taken from one piece of monocrystal wafer, resulting into large increase of the manufacturing cost.
Moreover, it is another approach to dispose an optical lens ahead of a photo detector to condense the light striking against the lens to the photo detector. This photo detector needs a large optical lens, and the thickness is increased by the spacing between the photo detector and the lens, whereby the element becomes a large-scale.